The AR8MM Arbor is used with Aimshot"s .223 Laser Bore Sight specifically for the following calibers: - 264 Win, 300 Win, 7mm Mag, 300 Weatherby, 270 Weatherby, 7mm Weatherby, 340 Weatherby, 257 Weatherby, 8mm, .358 Norma Mag, .308 Norma Mag, .416 Rem Mag, 7mm Shooting Times Westerner. It is made of 100% brass for durability and quality.